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Article

Mechanical and Hygrothermal Properties of Zeolite-Modified Pervious Concrete in Hot and Humid Area

by
Kaiwen Guo
1,*,
Shiping Guo
2,
Xingji Chen
2 and
Qianlong Qi
3
1
Manchester School of Architecture, The University of Manchester, Oxford Rd, Manchester M13 9PL, UK
2
Jiangsu Shibo Design & Research Institute Co., Ltd., Xuzhou 222023, China
3
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(3), 2092; https://doi.org/10.3390/su15032092
Submission received: 19 December 2022 / Revised: 15 January 2023 / Accepted: 18 January 2023 / Published: 22 January 2023
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Versions Notes

Abstract

:
Pervious concrete has good permeability and moisture adjustment properties due to its rich pore structure. It can not only reduce surface runoff by infiltration of rainfall, but also retain a certain amount of water inside, and then decrease the surface temperature via evaporation. In order to optimize the evaporative cooling performance of pervious concrete, this study introduces a modified method of incorporating superabsorbent zeolite produced from industrial wastes into pervious concrete as hygroscopic filler. The effects of zeolite dosages on the basic physical and mechanical properties of pervious concrete were analyzed, and then the evaporative cooling performance of zeolite-modified pervious concrete with the optimum replacement rate was studied. The results showed that the zeolite addition significantly reduced the density of pervious concrete, while having little impact on the permeability. The compressive and splitting tensile strength of pervious concrete increased first and then decreased as the replacement rate of zeolite powder increased, and the content of 15% zeolite powder and 20% zeolite aggregate was beneficial to improve the mechanical properties of pervious concrete. Contributing to the abundant micro-pores and higher specific surface area of zeolite particles, this could improve capillary water absorption and the water storage ability of pervious concrete. During the process of evaporation, the water absorption increment could effectively reduce the surface temperature by 5–8 °C, and maintain the evaporation cooling effect for 10–12 h.

1. Introduction

The continuous expansion of the urban scale results in the over-artificialization of the urban underlying layer, which disrupts the balance of heat and humidity exchange between the natural soil interface and the atmosphere [1,2,3]. The majority of existing pavement is made of impervious materials such as asphalt, concrete and cement brick, which have lost their ability to adjust to surface temperature and humidity [4]. In addition to concrete’s thermal inertia, the heat absorbed by impervious pavement during the day will be released as long-wave radiation at night, increasing the average air temperature near the surface and exacerbating the urban heat island effect [5,6]. Furthermore, a large amount of vegetation and lawns are being replaced by impervious pavement, causing rain to be unable to penetrate the ground quickly, resulting in urban waterlogging. Therefore, how to alleviate the deterioration of the urban environments caused by artificially hardened underlying surface has become an urgent problem to be solved.
Pervious concrete pavement, as a common surface material for the underlying surface in sponge city construction, has multi-scale pore structure characteristics (porosity of 15–30%). These pore structure not only allow rainwater runoff to penetrate into the base to promote groundwater recharge, but also intercept part of the water for evaporation and cooling on hot days, providing a double ecological benefit in alleviating urban waterlogging and the urban heat island [7,8]. Permeable pavement has become increasingly popular in hot and humid areas of southern China, where it is widely used in plazas, greenways, parks and other major outdoor activity areas for people, thanks to the rapid development of sponge city construction [2,9]. However, compared with permeability, the evaporative cooling performance of pervious concrete is still being questioned. The problem lies in the fact that the excessive penetration rate of pervious concrete can not effectively store water in the material for subsequent evaporation [2,3].
To further optimize the evaporative cooling performance of pervious concrete, there are three commonly used improvement measures: (i) optimizing the porous structure; (ii) providing an effective water supply; and (iii) adding water-retentive fillers. For the first scenario, Qin et al. [10] closed the sides and bottom of pervious concrete and inserted an overflow pipe with the same thickness as the paving material into the material, which not only ensured water penetration, but also intercepted enough water for evaporation and cooling. In terms of effective water source supplement, Yamagata et al. [11] conducted a drenched-water cooling test on permeable pavement and found the pavement temperature decreased by 8 °C in the daytime and 3 °C at night. In comparison with the previous two measures, the optimal design of pore structure is easily limited by its own mechanical properties, whereas effective water supplementation must be based on pervious concrete’s water retention performance. When water evaporates from the road surface, the porous structure of water-retaining fillers such as pulverized biochar [2,3,12], aporous geopolymers [13], fiber [14] and blast furnace slag [15] can transport water from the bottom through capillary channels, allowing the pavement to remain at a low temperature for a longer period of time. Thus, water-retentive filler is considered to be the most feasible strategy.
Natural zeolite is a porous silica-aluminate crystal material with an abundant pore structure and specific surface area, resulting in high hydrophilicity and absorbability. Studies showed that adding zeolite powder into cement mortar significantly improved its humidification ability, so it is widely used in the field of building materials [16]. Furthermore, it has been found that zeolite powder can be used as a potential auxiliary cementing material to replace cement, and that within a certain range of dosage; it can improve the mechanical and durability properties of cement composite materials [17,18,19]. For example, Nas et al. [20] found that zeolite powder can improve the strength of concrete, and the porosity of concrete increases with the increase in zeolite content. Similar results have been reported that zeolite powder can replace part of the cement in green concrete without affecting the strength of concrete, and the compressive strength is improved when zeolite replaces the cement by 15% [21]. Moreover, owing to its abundant and complicated micro-pore structure, the maximum amount of water zeolite particles can absorb is 2–3 times their own mass, in theory [22]. Zhou et al. [11] reported the humidity control performance optimization of zeolite-based composite humidity control material and found that the hygroscopic moisture content changed rapidly when the relative ambient humidity remained stable in the range of 50–60%. The above characteristics are helpful to improve the hygrothermal properties of cement composites with zeolite added. However, the influence mechanism of zeolite particles on the water absorption and evaporation process of pervious concrete is rarely reported, which severely limits the popularity and application of zeolite in pervious concrete [2].
To fill this gap, super absorbent zeolite was used to replace part of the cement or aggregate to prepare pervious concrete in this paper, and the influence of different zeolite contents on the basic physical and mechanical properties of pervious concrete was investigated, and the influence of evaporation cooling performance of zeolite modified permeable concrete at the optimum replacement rate was further investigated. This research is important for optimizing the hygrothermal properties of pervious concrete and mitigating the urban heat island effect, as well as for promoting the use of industrial wastes in a sustainable way.

2. Materials and Methods

2.1. Materials and Mix Design

The raw materials used in this study were cement, coarse aggregate, river sand, zeolite, water and superplasticizer. Portland cement (P.O 42.5) was produced from Long ‘an Conch Cement Co., LTD (Nanning, China), and its physical properties are shown in Table 1. Coarse aggregate and river sand were used in the tests, and their main properties have been discussed previously [6]. Two kinds of zeolites, namely coarse zeolite and fine zeolite, obtained from mineral deposit wastes, were utilized to produce zeolite-modified pervious concrete. The polycarboxylic acid superplasticizer produced by Shandong Gaoqiang New Material Technology Co., Ltd. (Linyi, Shandong, China) was used to improve the workability of pervious concrete.
As shown in Figure 1, zeolite particles have sizes of 3–5 mm and 100 mesh, respectively. Morphologies of pulverized zeolite were examined by a scanning electron microscope (Figure 2). One can observe that it is elongated and fibrous in shape with abundant macro-pores of size 10–30 μm on the surface, and these distributions are active in absorption and retention of water in the initial hardening [23].The chemical compositions of zeolite powder are shown in Table 2.
The mix of pervious concrete samples was designed with the volume method in accordance with CJJ/T135-09 [24]. Zeolite-modified pervious concretes were prepared in the experiment. In addition, pervious concrete without zeolite was prepared as the control pervious concrete (CK). Zeolite particles were incorporated at different levels to partially replace the cement or coarse aggregate with equivalent volume method, respectively. When zeolite particles substitute for cement mass, the replacement levels were 5%, 10%, 15% and 20%, respectively; while zeolite particles replace coarse aggregate mass, the replacement levels were 10%, 20%, 30% and 50%, respectively.
According to the past experience of our research group [6], the mix ratio used in this study was as follows: the coarse aggregate particle size was 4.75–9.50 mm, porosity of 25%, and the water-binder ratio was 0.30. In order to improve workability of pervious concrete, superplasticizer was used and the dosage was 0.8% of the cementitious material mass. The mix proportions are shown in Table 3.
The following samples with specific mix proportions were planned: for the water absorption tests, three standard test blocks of 100 × 100 × 100 mm were prepared (Figure 3a); for the compressive strength and splitting tensile strength tests, three cylindrical test blocks with a base diameter of 100 mm and a height of 200 mm were prepared (Figure 2b). Similarly, for the evaporative cooling experiment, three blocks of 300 × 300 × 60 mm were prepared (Figure 3c). After preparation, all of the samples were demoulded for 48 h before being cured in a standard room with a temperature of 20 °C and a relative humidity of 95%.

2.2. Experimental Methods

Table 4 shows the performed tests as well as the relevant standards. All the tests use at least three samples.
In order to investigate the effect of zeolite on evaporative cooling performance of pervious concrete brick, the first test section of wind tunnel test platform in hot and humid climate was selected for evaporative cooling test. The wind tunnel is a vertical backflow wind tunnel with two test sections: thermal and humid environment of materials and atmospheric boundary layer. The first test section can simulate the performance of building materials, components and modules under various environmental conditions. The second test section can simulate neutral and non-neutral atmospheric boundary layers, which can be used to study urban heat islands, regional planning and other topics. The first test section is 3.0 × 2.5 × 6.0 m (width × length × height). Along the airflow direction are the temperature stratification device, turbulence generator, heat and cold radiant plate and model turntable with a diameter of 2.4 m. The platform can precisely recreate any complex meteorological parameter environment. More specific design parameters of the wind tunnel have been introduced in our previous research [3].
To minimize the influence of meteorological parameters on the evaporative cooling effect of pervious samples as much as possible, steady-state conditions were adopted in the test process. The meteorological parameters were set to reflect typical weather in Guangzhou solar radiation of 600 W/m2, relative humidity of 60%, wind speed of 1.5 m/s and air temperature of 33 °C. The temperature of air conditioning chamber was controlled at 20 °C to simulate underground constant temperature. In addition, three BW32KH series electronic scales (measuring range 0–32 Kg, accuracy 0.01 g) with continuous automatic reading were installed in the lower part of the wind tunnel test section to monitor the change in evaporation of pervious samples. The samples to be tested were placed in an acrylic square box with polyethylene foam board wrapped around the four sides and bottom. To ensure one-dimensional heat transfer, the surface of the specimen was adjusted to be consistent with the illumination of the light source by adjusting the height of the Ⅱ-shaped steel connector below the acrylic box (Figure 4 and Figure 5). The electronic balance was linked to the computer via a professional transmission line and automatically recorded the specimen’s mass changes every minute. To monitor the temperature change of the sample, a high-precision T-type thermocouple line was placed on its surface. To monitor the temperature change of the sample, a high-precision T-type thermocouple line is placed on its surface. The thermocouple line was adhered to the specimen’s surface with heat-conducting silica gel and the other end was connected to a data acquisition instrument. The total duration of the evaporation experiment was 48 h, and the curing age of all samples was 28 days. Before evaporation, all samples were soaked in distilled water until saturation.

3. Results and Discussion

3.1. Density, Porosity and Permeability

The density and porosity of pervious concrete can indirectly reflect its compactness. Figure 6a shows the variation trend of porosity and density of 28d pervious samples with a zeolite powder dosage. As the zeolite powder content increases, the volume density of the sample decreases slightly. For example, increasing the zeolite powder content from 0% to 20% can reduce the sample density by up to 260 kg/m3. This is because the specific gravity of zeolite powder (approximately 736 kg/m3) is lower than that of Portland cement. However, an addition of 5% of zeolite powder shows the highest density value of about 2170 kg/m3, which means an increase in density by 10% compared with that of the CK samples, which could be due to the fact that replacing part of the Portland cement with fine particles can improve the compactness of cementitious materials through internal curing. This phenomenon can be explained by the strength analysis results. The porosity of all the samples varies between 22 and 30% as the zeolite powder content increases, and there is no significant correlation between the two. As a result, the effect of the zeolite powder addition on the porosity of pervious concrete can be regarded as random. This finding is consistent with Qin et al. [30], who believed that the porosity of pervious concrete is controlled by the large pores between aggregates and less by the type of the cement binder.
The zeolite aggregate modification group’s results show a similar but slightly different trend. The porosity of the ZP2 group ranges from 25 to 32%, and the volume density ranges from 1990 to 2160 kg/m3. Compared with the CK group, the addition of 50% zeolite aggregate increases porosity by 12%. The increase in porosity is possibly attributed to the porous structure of the zeolite aggregate, as well as the large holes and cracks around the ITZ in the concrete.
The relationship between different zeolite powders, zeolite aggregate substitution rates and the permeability coefficient of pervious concrete is further analyzed in Figure 7a. For example, the permeability coefficient of the reference group is approximately 3.41 mm/s, and the permeability coefficient of the ZP1 group is between 3.37 and 3.78 mm/s, with no significant difference in the change of the permeability coefficient of each sample as the replacement rate of zeolite powder increases. Unlike the ZP1 group, the influence of the zeolite aggregate on the permeability coefficient is fairly consistent. The permeability coefficient of the ZP2 group fluctuates in the range of 3.48~4.97 mm/s, and increases with zeolite aggregate dosages.
Although the effect of zeolite incorporation on the porosity and permeability coefficient of pervious concrete is random, there is a relationship between the permeability and the porosity. The permeability of pervious samples is found to increase linearly with the porosity (Figure 7b and Figure 8b), which is consistent with the previous study’s findings [30].

3.2. Compressive and Splitting Tensile Strength

3.2.1. Compressive Strength

Figure 9a shows the compressive strength of pervious concrete with varying zeolite contents after 28 days. With the increase in zeolite content, the compressive strength of each permeable specimen first increases and then decreases. For example, the 7-day strength of pervious concrete with 10%, 15% and 20% zeolite powder content is 103.03%, 105.71% and 87.37%, respectively, of the reference group. The compressive strength of concrete with 5%, 10%, 15% and 20% zeolite powder increases with age by 26.45%, 27.85% and 24.87%, respectively, indicating that the addition of zeolite powder contributed to the improvement of concrete strength at the later stage of hydration. This could be because, after replacing the same amount of cement with zeolite powder, the content of the hydration product calcium hydroxide gradually increases, and the active ingredients in zeolite powder (SiO2 and Al2O3) undergo a secondary hydration reaction with Ca(OH)2, which improves the compressive strength of concrete in the later stage [19].
The compressive strength of pervious concrete with different zeolite aggregate replacement rates is shown in Figure 9b. It can be seen that the compressive strength of pervious concrete decreases with an increasing zeolite aggregate replacement rate, regardless of age. The compressive strength of pervious concrete at 7 days is equivalent to that of plain concrete when the aggregate replacement rate is 10%. At 7d age, the compressive strength of pervious concrete with 20%, 30% and 50% zeolite aggregate content is 95.03%, 92.71% and 87.37% of that of the reference group, respectively. When compared with the control group, the compressive strength of the 28d age group decreased by 2.1% to 11.2%. This is primarily due to two factors: (1) The strength of pervious concrete is primarily determined by coarse aggregate extrusion and the strength of cement slurry at the bonding point between aggregates. Because zeolite aggregate has a lower hardness than coarse aggregate, the strength of pervious concrete decreases when the same amount of aggregate is replaced with zeolite aggregate; (2) Zeolite has a strong attraction to polar water molecules. The pores and pipes within zeolite can absorb a large amount of water, resulting in a decrease in free water in the matrix, which affects hydration and thus the mechanical properties of pervious concrete [17].

3.2.2. Splitting Tensile Strength

Figure 10a compares the splitting tensile strength of pervious concrete with different zeolite powders. The splitting tensile strength and compressive strength development trends are somewhat different. The splitting tensile strength of pervious concrete mixed with zeolite powder is lower after 7 days than that of the plain one. The splitting tensile strength of pervious concrete decreases with increasing zeolite powder content at the age of 28 days. For example, the splitting tensile strength of 5%, 10% and 15% zeolite powder replacement rates increases by 1.4%, 5.6% and 7.88%, respectively, but the splitting tensile strength of the 20% replacement rate decreases by 8.7%, indicating that the addition of zeolite powder will lead to the decline of early splitting tensile strength and promote the improvement of later strength to some extent.
Figure 10b shows the splitting tensile strength of pervious concrete in the ZP2 group. When compared with the control sample, the 10% and 20% additions of zeolite aggregate result in an increase in 7d splitting tensile strength by 4.8% and 2.9%, respectively. However, further increasing the zeolite aggregate dosage reduces the splitting tensile strength, and 30% and 50% of zeolite aggregate resulted in a reduction in 7d strength by 4.81% and 12.5%, respectively. A similar trend is observed in the 28d strength results. When considering the economic benefit, the cheaper zeolite powder has obvious advantages and can effectively reduce the project cost. As a result, the content of 15% zeolite powder and 20% zeolite aggregate is superior in terms of mechanical properties.

3.3. Water Absorption Properties

The water absorption process of porous materials can be divided into two stages based on the cumulative water absorption curve: rapid water absorption and stable water absorption periods. According to ASTM C1585 [27], the vertical coordinate is the water absorption I (kg/m2) and the horizontal coordinate is the square root of time t (s1/2). In the first stage, the slope obtained by the linear fitting of the initial 6 h test data was defined as the initial sorptivity S1. The second stage is the stable water absorption stage. Water gradually penetrates the pores of the material, reducing the capillary water absorption capacity. Furthermore, the resistance along the pore increases, making it difficult for water to quickly fill these smaller pores, resulting in a slow water absorption process at this stage. Linear fitting of 6–192 h test data yielded the secondary sorptivity S2.
Figure 11 shows the water absorption profiles and the deviation of the 28-day pervious samples with different zeolite types. The water absorption profiles exhibit the characteristics of a fast water absorption rate in the early stage but relatively slow one in the later stage. It is found that the capillary water absorption of each specimen increased as the time increased, but the rate of water absorption growth was significantly different due to the influence of zeolite particle size. In the ZP1 group, the total capillary water absorption of pervious concrete first decreases and then increases as the zeolite powder content increases. The water absorption of pervious concrete with less than 5% content is lower than that of the CK sample. However, further increasing the amount of zeolite powder will increase the capillary water absorption, and 10% and 20% zeolite powder will increase the water absorption by 15.7% and 27.6% respectively.
A similar but slightly different phenomenon is reflected in the ZP2 group results. The cumulative total water absorption of the specimen gradually increases with increasing zeolite aggregate content. For instance, compared with the zeolite-free one, the addition of 10%, 20%, 30% and 50% of zeolite aggregate increases the water absorption by 16%, 22%, 30% and 39%, respectively. The improvement in the water absorption may be linked to the voids and networks created by the zeolite aggregate in concrete. This finding was also found by Tan and Gupta et al. [23,31], who believed that the increased water absorption is related to the internal pore structure of concrete.
Figure 12 and Figure 13 further compare the zeolite content’s influence law on the capillary water absorption coefficient of pervious concrete. It is found that the initial sorptivity rate S1 of each specimen increases linearly with the zeolite powder content (R2 > 0.90). As mentioned above, although a small number of zeolite powder particles reduces the porosity inside the concrete, the pores of the zeolite itself may play a dominant role in the water absorption process. In contrast, no clear linear relationship was found between the zeolite content and the secondary sorptivity rate S2 (R2 = 0.84). Furthermore, the slope value of pervious concrete in the zeolite powder system is greater than that of the specimen in the zeolite aggregate system. For example, the mean values of S1 and S2 of ZP1 and ZP2 specimens were 22.49 × 10−3 kg/(m2·s2), 20.34 × 10−3 kg/(m2·s2) and 1.74 × 10−3 kg/(m2·s2), 1.56 × 10−3 kg/(m2·s2), respectively, indicating that the increase in zeolite powder fineness has a greater effect on the capillary of pervious concrete, which can be explained by the fine zeolite powder particles having higher specific surface areas.

3.4. Evaporative Cooling Properties

3.4.1. Evaporation Profile

The evaporation process of permeable material after water absorption saturation can be divided into two stages. The vapor pressure difference in the surrounding environment drives the evaporation in the first stage, and capillary action transports water from the saturated zone to the evaporation surface. The second evaporation stage mainly takes place in the material medium. As the evaporation of free water occurs on the surface, the free water in the pores also begins to evaporate. Internal water vapor diffuses to the surface through molecular diffusion, and then evaporates into the air in the process [2].
Figure 14 compares the hourly evaporation rates and the cumulative evaporation of the zeolite-modified pervious concretes under steady-state wind tunnel conditions. As can be seen from Figure 14a, the maximum initial evaporation rate of ZP1-10 and ZP2-15 samples is 0.54 kg/(m2·h) and 0.48/kg/(m2·h), respectively, while the evaporation rate of the PC sample is only 0.42 kg/(m2·h). This is because the evaporation rate in the first stage is primarily determined by the capillary water absorption rate and the volume water content in the material’s pores. A higher water absorption rate material can maintain a longer hydraulic balance in the pores, thus ensuring that water migrates to the surface and evaporates relatively easily. Water supply can be increased by using materials with a higher saturated volume water content. The addition of zeolite can improve the structure of pervious concrete’s medium-large pores. These pores absorb water quickly via capillary force, can maintain hydraulic continuity over long distances and can effectively extend the evaporation time of the first stage of pervious concrete. As a result, the first evaporation stage of ZP1-10 and ZP2-15 can last 8 h and 6 h, respectively, whereas the first evaporation stage of PC can last only 2 h. The evaporation force decreases sharply in the second evaporation stage due to viscous force and downward gravity, and the evaporation rate of all samples decreases sharply. After 20 h, the evaporation rate of the three previous samples drops to about 0.1 kg/(m2·h), and the evaporation rate stabilizes.
As shown in Figure 14b, zeolite as an absorbent filler can increase the cumulative evaporation of pervious concrete. The cumulative evaporation of ZP1-10 and ZP2-15 is about 0.59 kg and 0.51 kg, respectively, which is 30–40% larger than that of samples without zeolite. The possible reason is that large pores of zeolite particles adsorb a lot of free water. In conclusion, capillary water absorption has a significant impact on the evaporation process of pervious materials. This suggests that incorporating zeolite particles into pervious concrete can improve the internal capillary interstice structure, effectively maintaining hydraulic continuity over a long distance.

3.4.2. Surface Temperature

Figure 15 shows the average surface temperature changes of the three permeable materials 48 h after water absorption saturation. It can be seen that in the wet state, the pervious material can effectively remove heat absorbed by its surface via the evaporation of latent heat, thus reducing the surface temperature. In contrast, under the same heat source, the temperature of ZP1-10 and ZP2-15 rose slower than that of PC in the early stage, with maximum temperature drops of 8 °C and 5 °C, respectively. Through a further comparison of surface temperature and the evaporation rate of the three pervious materials, it is found that ZP1-10 and ZP2-15 can maintain relatively low temperatures for approximately 12 h and 10 h, respectively. Compared with the PC specimen with poor capillary water absorption performance, zeolite particles with strong capillary action can transport more free water to the surface, effectively extending the evaporation time of the first stage. The surface temperature results confirm that incorporating zeolite particles into pervious concrete can increase the evaporation rate and time of the first stage, thereby increasing the evaporation rate and prolonging the evaporation cooling effect.

4. Conclusions

By adding superabsorbent zeolite to replace part of the cement or aggregate to prepare pervious concrete, the influence of zeolite dosages on the basic physical and mechanical properties of pervious concrete were analyzed, then the evaporative cooling performance of the zeolite-modified pervious concrete were studied at the optimum replacement rate. The results of this study are as follows:
(1) Increasing the zeolite powder content from 0% to 20% decreases the bulk density of the pervious concrete by 260 kg/m3 at the maximum. The influence of the addition of zeolite on the permeability coefficient is random, which may be related to the heterogeneity of pervious concrete.
(2) The compressive and splitting tensile strength of pervious concrete increases first and then decreases as the replacement rate of zeolite powder increases. When the replacement rate is less than 5%, the strength of zeolite-modified pervious concrete can be not lower than that of the control. Zeolite powder can increase the compressive strength of concrete at the later stage by up to 16%. However, the compressive strength of pervious concrete decreases with the increase in the replacement rate of zeolite aggregate. As a result, the content of 15% zeolite powder and 20% zeolite aggregate is excellent in mechanical properties.
(3) As the dosage of zeolite powder is increased, the total capillary water absorption of pervious concrete decreases first and then increases. Water absorption is lower in pervious concrete with a dosage of less than 5% than in the reference specimen. However, 10% and 20% zeolite powder will increase the water absorption by 15.7% and 27.6%, respectively. When zeolite particle is used instead of coarse aggregate, the cumulative total water absorption of the specimen increases gradually with the zeolite content. Zeolite powder is superior to zeolite aggregate in improving capillary water absorption.
(4) The addition of zeolite particles can significantly increase the accumulated evaporation of pervious concrete. Under the same heat source, the temperatures of ZP1-10 and ZP2-15 rise slower than those of PC in the early stage, with maximum temperature drops of 8 °C and 5 °C, and they maintain the low temperature time for 12 h and 10 h, respectively.
Overall, adding zeolite into the pervious concretes can achieve better hydrological and thermal properties, which is beneficial for improving the evaporative cooling effect of pervious pavement. In the future, one can choose to add a water reducing agent, or to mix zeolite with other aggregate gradations and admixtures, so as to further increase the substitution amount of zeolite while meeting the mechanical property requirements.

Author Contributions

Investigation, Q.Q.; Writing—original draft, K.G.; Writing—review & editing, S.G.; Supervision, X.C. All authors have read and agreed to the published version of the manuscript.

Funding

The author would like to thank the Jiangsu Provincial Construction System Science and Technology Projects and Technology Demonstration Projects (2016JH15).

Conflicts of Interest

The author declares no conflict of interest.

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Figure 1. Zeolite particles have different sizes (a) coarse zeolite of 3–5 mm, (b) zeolite powder of 100 mesh.
Figure 1. Zeolite particles have different sizes (a) coarse zeolite of 3–5 mm, (b) zeolite powder of 100 mesh.
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Figure 2. SEM micrograph of pulverized zeolite particles.
Figure 2. SEM micrograph of pulverized zeolite particles.
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Figure 3. Zeolite-modified pervious concrete samples (a) samples for the water absorption tests, (b) samples for the strength tests, (c) Samples for evaporative cooling experiment.
Figure 3. Zeolite-modified pervious concrete samples (a) samples for the water absorption tests, (b) samples for the strength tests, (c) Samples for evaporative cooling experiment.
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Figure 4. Three specimens were subjected to evaporation cooling experiment in the wind tunnel device (a) the interior o CWT, (b) the detail of samples arrangement.
Figure 4. Three specimens were subjected to evaporation cooling experiment in the wind tunnel device (a) the interior o CWT, (b) the detail of samples arrangement.
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Figure 5. Device for automatically collecting sample evaporation (a) top view, (b) section view.
Figure 5. Device for automatically collecting sample evaporation (a) top view, (b) section view.
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Figure 6. Open porosity and bulk density of zeolite-modified pervious samples at 28d age with different replacement (a) zeolite powder, (b) zeolite aggregate.
Figure 6. Open porosity and bulk density of zeolite-modified pervious samples at 28d age with different replacement (a) zeolite powder, (b) zeolite aggregate.
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Figure 7. The permeability of pervious concrete with different zeolite powder dosages (a); the correlation between permeability and porosity (b).
Figure 7. The permeability of pervious concrete with different zeolite powder dosages (a); the correlation between permeability and porosity (b).
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Figure 8. The permeability of pervious concrete with different zeolite aggregate dosages (a); the correlation between permeability and porosity (b).
Figure 8. The permeability of pervious concrete with different zeolite aggregate dosages (a); the correlation between permeability and porosity (b).
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Figure 9. Compressive strength of zeolite-modified pervious samples at 7/28 days with different replacement (a) zeolite powder, (b) zeolite aggregate.
Figure 9. Compressive strength of zeolite-modified pervious samples at 7/28 days with different replacement (a) zeolite powder, (b) zeolite aggregate.
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Figure 10. Splitting tensile strength of zeolite-modified pervious samples at 7/28 days with different replacement (a) zeolite powder, (b) zeolite aggregate.
Figure 10. Splitting tensile strength of zeolite-modified pervious samples at 7/28 days with different replacement (a) zeolite powder, (b) zeolite aggregate.
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Figure 11. Effect of zeolite content on cumulative water absorption of specimens (a) Zeolite powder, (b) Zeolite aggregate.
Figure 11. Effect of zeolite content on cumulative water absorption of specimens (a) Zeolite powder, (b) Zeolite aggregate.
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Figure 12. Effect of zeolite powder dosage on sorptivity of specimen (a) initial sorptivity, (b) secondary sorptivity.
Figure 12. Effect of zeolite powder dosage on sorptivity of specimen (a) initial sorptivity, (b) secondary sorptivity.
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Figure 13. Effect of zeolite aggregate content on sorptivity of specimen (a) initial sorptivity, (b) secondary sorptivity.
Figure 13. Effect of zeolite aggregate content on sorptivity of specimen (a) initial sorptivity, (b) secondary sorptivity.
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Figure 14. Evaporation profiles of zeolite-modified pervious concrete (a) hourly evaporation rate, (b) cumulative evaporation.
Figure 14. Evaporation profiles of zeolite-modified pervious concrete (a) hourly evaporation rate, (b) cumulative evaporation.
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Figure 15. Surface temperature of zeolite-modified pervious concrete under wet conditions.
Figure 15. Surface temperature of zeolite-modified pervious concrete under wet conditions.
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Table
Table 1. Physical properties of Portland cement.
Table 1. Physical properties of Portland cement.
Specify Gravity (g/cm3)Blaine Specific Surface (m2/kg)Setting Time (min)Compressive Strength (MPa)
Initial SettingFinal Setting3 d28 d
3.0936412420338.550.2
Table
Table 2. Chemical composition of zeolite powder and Portland cement.
Table 2. Chemical composition of zeolite powder and Portland cement.
Chemical Composition (%)CaOSiO2Al2O3Fe2O3MgOK2ONa2OSO3
Cement63.9221.084.543.651.760.730.582.05
Zeolite1.9866.2812.720.680.452.982.250.34
Table
Table 3. Mix proportions of pervious concrete (kg/m3).
Table 3. Mix proportions of pervious concrete (kg/m3).
Mix IDCementAggregatesWaterCoarse ZeoliteFine ZeoliteSandWater Reducer
CK302.01509.0105.700167.71.4
ZP1-5286.91509.0105.7-15.1167.71.4
ZP1-10271.81509.0105.7-30.2167.71.4
ZP1-15256.71509.0105.7-45.3167.71.4
ZP1-20241.61509.0105.7-60.4167.71.4
ZP2-10302.01358.1105.7150.9-167.71.4
ZP2-20302.01207.2105.7301.8-167.71.4
ZP2-30302.01056.3105.7452.7-167.71.4
ZP2-50302.0754.5105.7754.5-167.71.4
Table
Table 4. Test program and relevant standards.
Table 4. Test program and relevant standards.
PropertyStandard FollowedRemarks
Hardened densityASTMC1699 [25]
Porosity
PermeabilityASTM C1701 [26]The water permeability of the samples was tested using a constant head method. Here, the water head difference across the sample was 6 cm.
Water absorption and
sorptivity		ASTM C1585 [27]To measure the water absorption, we cut the specimen into a shape with 100 × 100 × 60 mm3, sealed the four sides and top of it with the waterproof tape, and then placed the specimen above a water bath with the bottom of it approximately 3–5 mm contact with the water.
Compressive strengthASTM C39 [28]
Splitting tensile strengthASTM C496 [29]
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Guo, K.; Guo, S.; Chen, X.; Qi, Q. Mechanical and Hygrothermal Properties of Zeolite-Modified Pervious Concrete in Hot and Humid Area. Sustainability 2023, 15, 2092. https://doi.org/10.3390/su15032092

AMA Style

Guo K, Guo S, Chen X, Qi Q. Mechanical and Hygrothermal Properties of Zeolite-Modified Pervious Concrete in Hot and Humid Area. Sustainability. 2023; 15(3):2092. https://doi.org/10.3390/su15032092

Chicago/Turabian Style

Guo, Kaiwen, Shiping Guo, Xingji Chen, and Qianlong Qi. 2023. "Mechanical and Hygrothermal Properties of Zeolite-Modified Pervious Concrete in Hot and Humid Area" Sustainability 15, no. 3: 2092. https://doi.org/10.3390/su15032092

APA Style

Guo, K., Guo, S., Chen, X., & Qi, Q. (2023). Mechanical and Hygrothermal Properties of Zeolite-Modified Pervious Concrete in Hot and Humid Area. Sustainability, 15(3), 2092. https://doi.org/10.3390/su15032092

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